Embodiments of the present subject matter generally relate to the deposition of reactively sputtered thin films on substrates. Exemplary films may be composed of two or more elements including, but not limited to, metal oxides, nitrides and carbides utilized to form non-scattering coatings, scattering coatings, and wear coatings. Exemplary substrates may be, but are not limited to, tungsten-halogen incandescent lamps, solar mirrors, lamp reflectors, lamp burners, and drill bits. Prior art coating systems for these substrates generally utilize magnetron sputtering systems. FIGS. 1 and 2 are perspective views of prior art magnetron sputtering systems. With reference to FIG. 1, conventional magnetron sputtering systems utilize a cylindrical, rotatable drum 2 mounted in a vacuum chamber 1 having sputtering targets 3 located in a wall of the vacuum chamber 1. Plasma or microwave generators 4 known in the art may also be located in a wall of the vacuum chamber 1. Substrates 6 may be removably affixed to panels or substrate holders 5 on the drum 2. With reference to FIG. 2, a plurality of substrates 6, such as lamp burners, may be attached to the rotatable drum 2 via a conventional substrate holder 8. Conventional substrate holders 8 generally include a plurality of gears and bearings 9 allowing one or more lamps 6 to rotate about its respective axis. Material from the sputtering target 3 may thus be distributed around the lamps 6 as they pass a target 3. Obtaining sufficient uniformity in coating generally requires plural rotations past the target 3. Sputtering systems according to embodiments of the present subject matter may move the substrates rapidly and/or repeatedly past the sputtering target so as to limit the material deposited in a single pass to no more than a few atomic mono-layers, and often less than one. Exemplary single-pass material thicknesses may range from about one to thirty angstroms.
Much of the required oxidation in these conventional sputtering systems may occur contemporaneously with the metal deposition past the target, which is usually, but not necessarily, made of a single metal. For clarity purposes, oxidation may be generally defined as the loss of one or more electrons by an atom, molecule, or ion during a chemical reaction. Oxidation is generally accompanied by an increase in the oxidation number on the atoms, molecules, or ions that lose electrons. In embodiments of the present subject matter, oxidation may be completed in other parts of the respective vacuum chamber during the intervals between deposition passes. Oxidation in embodiments of the present subject matter may be conducted with or without the aid of a highly oxidizing source, e.g., a microwave-driven plasma.
One limitation of prior art sputtering systems is the onset of incomplete oxidation as average deposition rates are increased. To avoid incomplete oxidation in conventional systems, power must be limited to the sputtering targets resulting in a reduction of the overall throughput of the system. Further, in systems including oxides requiring transmission in the visible range, this incomplete oxidation may generally be manifested as an absorbing film. Accordingly, there is a need in the art for an exemplary thin film coating method and system that overcomes the shortcomings of the prior art. There is also a need in the art to increase the deposition rate of rutile titania on tungsten-halogen lamps and other substrates without introducing excess absorption.